The present invention relates to a method for manufacturing a tire carcass comprised of multiple plies, especially for a vehicle tire, by winding plies onto a winding drum with the following steps:
a) Providing a liner made of an air-impermeable rubber ply; PA1 b) Applying a ply onto the liner, whereby the ply material is comprised of plastic cords embodied in rubber material which plastic cords, before embedding, have been stretched under heating, whereby the beginning and the end of the applied ply overlap; PA1 c) Positioning the bead cores; PA1 d) Folding the lateral edges of the ply onto the bead cores; and PA1 e) Applying lateral strips etc. and enveloping the bead cores. PA1 providing a liner consisting of an air-impermeable material; PA1 preparing a carcass ply material by heating and stretching plastic cords and embedding the stretched plastic cords in rubber; PA1 placing a ply of the carcass ply material onto the liner with leading and trailing ply ends overlapping; PA1 heating the overlapping ply ends for returning stretched plastic cords into an unstretched state; PA1 positioning bead cores onto the ply; PA1 folding lateral edges of the ply over the bead cores; PA1 enveloping the folded lateral edges and the bead cores by lateral strips. PA1 a cutter including a cutting blade for cutting to length endless carcass ply material; PA1 a heat source positioned below the cutter and moveable upwardly into the vicinity of the endless carcass ply material; PA1 the heat source extending over at least a portion of the width of the endless carcass ply material and arranged for heating defined, identical zones of the endless carcass ply material located relative to a longitudinal extension of the cutting blade on both sides of the cutting blade.
Onto a thus created carcass the belt and the tread strip of the tire are applied subsequently by winding onto the tire building drum. Then, the green tire is vulcanized.
The individual plies are respective strips that are cut to length to be individually placed onto the tire building drum whereby the ends of each ply, in general, are overlaped in order to ensure that a closed strip in the circumferencial direction will result. The ply is comprised of a rubber layer which, in the direction of its width (transverse direction), includes reinforcing members in the form of cords. These cords may consist, for example, of rayon, polyester, or any other suitable plastic material. Polyester cords have the advantage, in comparison to rayon cords, that they are much less expensive. However, it is disadvantageous that they have a higher stretching capability. When the wound carcass is shaped, tensile forces act on the plies, respectively, its cords. Also, during vulcanization of the tire, tensile forces act on the cords so that they are being stretched. In order to ensure a uniform, defined stretching of the cords, they are stretched before being sent to a calender in order to be embedded in the rubber material whereby heat is applied for the stretching process. The amount of stretching of the stretched cords can be canceled by heating. Thus, upon heating the carcass ply material, a shrinkage of the ply may result. During vulcanization of the green tire in the heating press the reinforcement cords thus have the tendency to contract. This is prevented by the inner pressure provided by the bellows. After completion of vulcanization (without pressure within the bellows) an increased tensile stress results in the reinforcement cords which can be frozen (fixed) within the vulcanized rubber.
As a result of the aforedescribed tire building process the plies at the seam have an overlap of approximately 2 to 6 mm. Thus, the ply in this area has twice the material thickness, twice the density of cords (reinforcement members), and thus a different modulus of elasticity. At this location of the ply, a reduced stretching of the ply material thus takes place when tension forces are supplied. When a finished tire is inflated, the seam of the ply is thus visible as a constriction within the sidewall area. The quality and stability of the tire is not affected by this, but the visual appearance is impaired which, in general, is interpreted especially by laymen as a rupture within the carcass so that the tire is returned to the tire manufacturer or to the vehicle dealership.
It is therefore an object of the present invention to provide a method for manufacturing a carcass such that a constricted portion within the tire sidewall can be reliably prevented.